I’ve mentioned a number of custom components enhancing UIScrollView, such as ReorderableGridView for drag and drop reorderable views, and Refresher which makes it easy to add pull-to-refresh to a UIScrollView with custom animations.

Here’s an open source component that enhances UIScrollView with a number of added features called SMScrollView from Simon Hanukaev.

Specifically SMScrollView makes it easy to add centered zooming to a scroll view, double tap to zoom in and out, and scale to Fit for orientantion changes. An example project is included.